1. Field of the invention
This invention relates to relief valves and more particularly to a collapsible pin relief valve for fluid systems of relatively large diameter.
In the past, a collapsible pin relief valve has been successful, by utilizing Euler's law for slender columns to obtain the critical load point at which the column will fail by buckling, for monitoring pressure in a conductor generating a force up to approximately 8,000 pounds (3,600 kg) against the pin.
A collapsible pin in a two inch piston diameter pressure relief valve, connected with a conductor of the same size, containing 5,000 psi (2,250 kg) generates a force on the collapsible pin on the order of 15,000 pounds (6,750 kg). It is desirable to reduce this pin force without reducing the piston diameter.
There is a need for a valve to monitor such pressure in a large diameter, for example, a 24 inch (61 cm) conductor with a 24 inch piston opening, but this requires an unrealistically large diameter collapsible pin. When the outlet port of such a valve is connected with an elevated tank having a relatively high static fluid pressure some means must be provided for balancing the downstream back pressure acting on the piston members in order for the valve to function as desired in monitoring upstream fluid pressure.
This invention solves this problem by providing a collapsible pin relief valve in which piston-like members of different diameter partially balance the upstream pressure acting on the collapsible pin and completely balances the downstream pressure.
2. Description of the prior art
The most pertinent prior patent is believed to be U.S. Pat. No. 5,012,834 issued May 7, 1991 to Julian S. Taylor for FLUID PRESSURE FLARE RELIEF VALVE.
This patent discloses a valve body connected with a fluid line in which the valve body is enlarged and provided with a lateral opening normally closed by a double wall valve head to form a valve head chamber laterally of a fluid passageway through the valve body.
The fluid passageway contains a box-like chamber having aligned bores in opposite walls normally closed by dual pistons secured to a piston rod projecting through the valve head chamber and through the closed end of a cylinder projecting into the valve head chamber and slidably supporting a smaller diameter pilot piston secured to the piston rod.
The outwardly projecting end of the piston rod supports one end of an excess fluid pressure collapsible pin supported at its other end by the end plate of a pin cage surrounding the collapsible pin and connected with the cylinder projecting out of the valve head chamber.
A spring urged poppet valve admits upstream fluid pressure to the valve head chamber, so that excess pressure above a predetermined value against the pilot piston and the piston remote from the valve head chamber unbalances the pistons, collapsing the pin to release the excess pressure through the passageway downstream outlet.
This invention is distinctive over this patent by providing a valve housing having a flow passageway interposed in a conductor containing upstream and downstream fluid under greater than atmospheric pressure. A guide piston is slidably mounted in the valve housing for movement toward and away from the passageway outlet port and is axially connected with a smaller diameter outlet piston for closing the passageway outlet port. A piston rod connected with the guide piston projects outwardly of the valve body and abuts one end of a collapsible pin supported at is other end by a pin cage means secured to the valve housing.
Upstream fluid pressure in the valve housing acts on confronting surfaces of the pistons and the collapsible pin holds the outlet piston on seat while the force on the pin is proportional to upstream pressure. Downstream fluid pressure in the valve housing is balanced by the pistons.